13 Variety of Software ProcessesSoftware products are very varied...Therefore, there is no standard process for all software engineering projectsBUT successful software development projects all need to address similar issues.This creates a number of process steps that must be part of all software projects

14 Basic Process Steps in all Software Development• Feasibility and planning• Requirements• Design• Implementation• Acceptance and release• Operation and maintenanceIt is essential to distinguish among these aspects and to be clear which you are are doing at any given moment.Do not confuse requirements and design.

15 Feasibility and PlanningA feasibility study precedes the decision to begin a project.• What is the scope of the proposed project?• Is the project technically feasible?• What are the projected benefits?• What are the costs, timetable?A feasibility study leads to a decision: go or no-go.

16 Requirements Analysis and DefinitionThe requirements analysis and definition establish the system's services, constraints and goals by consultation with users. They are then defined in a manner that is understandable by both users and development staff.This phase can be divided into:Requirements analysisRequirements definitionRequirements specificationRequirements define the function of the system FROM THE CLIENT'S VIEWPOINT.

17 System and Program DesignSystem design: Partition the requirements to hardware or software systems. Establishes an overall system architectureSoftware design: Represent the software system functions in a form that can be transformed into one or more executable programsUnified Modeling Language (UML)The design describes the system FROM THE SOFTWARE DEVELOPERS' VIEWPOINT

18 Implementation ProgrammingThe software design is realized as a set of programs or program units. (Written specifically, acquired from elsewhere, or modified.)TestingIndividual components are tested against specifications.The individual program units are integrated and tested against the design as a complete system.

19 Acceptance and ReleaseThe complete system is tested against the requirements by the client.Delivery and releaseThe complete system is delivered to the client and released into production.

20 Operation and Maintenance: Software Life CycleOperation: The system is put into practical use.Maintenance: Errors and problems are identified and fixed.Evolution: The system evolves over time as requirements change, to add new functions or adapt the technical environment.Phase out: The system is withdrawn from service.

21 Combining the Process StepsFeasibility andPlanningRequirementsThere are many ways to combine the processesDesignOperation andMaintenanceImplementation

22 Sequence of ProcessesEvery software project will include these basic processes, in someshape or form, but:• They may be formal or informal• They may be carried out in various sequencesExamples:• A feasibility study cannot create a proposed budget and schedule without a preliminary study of the requirements and a tentative design.• Detailed design or implementation usually reveals gaps in the requirements specification.

24 Discussion of the Waterfall ModelAdvantages:• Process visibility• Separation of tasks• Quality control• Cost controlDisadvantages:Each stage in the process reveals new understanding of the previous stages, that requires the earlier stages to be revised.The Waterfall Model is not enough!

29 Process 3: Phased DevelopmentConceptA simple system with basic functionality is brought quickly into production (Phase 1).Subsequent phases are based on experience gained from users of each previous phase.AdvantagesPay-back on investment begins soon.Requirement are more clearly understood in developingsubsequent phasesExample: NSDL

32 Iterative Refinement + Waterfall Model: Graphics for BasicPhase 1: Implementation• When the final specification was agreed, the entire preprocessor and run-time support were coded from new.• The system was almost entirely bug-free.Phase 2: New compiler (Waterfall)Phase 1 was used as the requirements definition for thefinal version.

33 Observations about Software ProcessesCompleted projects should have the basic process stepsbut ... the development process is always partly evolutionary.Risk is lowered by:• Prototyping key components• Dividing into phases• Following a visible software process• Making use of reusable componentsConclusionIt is not possible to complete each step and throw it over the wall.

34 Project Presentations: Sequential OptionRequirementsFeasibility studyRequirements analysisDesignSystem designImplementationProgram designCodingTestingIf you follow a sequential process the three presentations should be as shown.AcceptanceOperation & maintenance